Grader

ABSTRACT

An endless conveyor grader (1) suitable for use in grading tubers (4) or the like. The endless conveyor comprises an endless grid screen (21) supported by an endless drive transmission (37) at opposite sides (23, 25) of the endless grid screen (21). An endless drive transmission guide (36, 39) is provided at opposite sides (23, 25) of the endless grid screen formed and arranged so as to define at least one cascade (40) or step (40) in the endless grid screen pathway. The cascade(s) or step(s) (40) allow for tumbling, in use of the grader of tuners (4) passing over the cascade(s) (40) or step(s) so as to provide the required movement of the tubers (4) on the grid screen (21) to facilitate the grading process. The grid screen comprises parallel support bars provided with a multiplicity of `I`-shaped link members (46) bridging between the support bars (47) so as to allow the grid screen to change direction in the endless grid screen pathway.

The present invention relates to a grader suitable for use in gradingand separating potatoes at harvest but not exclusively.

Separators have long been used to separate smaller seed potatoes fromlarger potatoes as well as separating stones, earth and other debriscollected during harvest. Grading, that is separating of potatoes moreor less accurately on the basis of their size, is of considerablecommercial importance for potato growers. For the producer of potatoesthe value of ware potatoes which generally have a diameter greater than55 mm, can be as little as one quarter of the value of seed potatoeswhich generally have a diameter within the range of from 35 to 55mm--below 35 mm diameter potatoes are generally not considered suitablefor use as seed. To the buyer of seed potatoes moreover the weight andhence cost of potatoes required for a given planting density will varyconsiderably with the size or diameter of the seed potatoes. There isaccordingly a need for accurate grading of potatoes and not only betweenseed and ware but also for particular size ranges of seed potatoes e.g.35 to 45 and 45 to 55 mm diameter. The sizing of seed potatoes isstrictly controlled by the United Kingdom Department of Agriculture, andother national agricultural institutions.

Presently known graders generally use either continuous screens made ofwire to form squares or sieve type screens which are both vibrated oroscillated vertically in an attempt to displace the potatoes thereonrelative to the screen thereby to facilitate passage of smaller potatoesthrough the screen to be collected separately from larger potatoes whichare carried further on by the screen to their own collecting point. Suchviolent agitation tends to cause the potatoes to jump up and down on thescreen whereupon the potatoes may be damaged when they fall back ontothe screen. Also such agitation is often of limited effectivenessinsofar as the potatoes simply fall back into their original position inwhich they were held from passing through the screen, and/or thepotatoes simply move up and down together with the screen so that thereis little or no displacement of the potatoes relative to the screen.Damaged potatoes stored with sound potatoes can give rise to rot whichcan subsequently damage healthy potatoes and are significantly lessattractive to prospective purchasers, be they wholesalers, shopkeepers,or ordinary shoppers, and it is therefore particularly important toavoid damage as far as possible.

It is an object of the present invention to avoid or minimise one ormore of the above disadvantages.

The present invention provides an endless conveyor grader suitable foruse in grading tubers or the like wherein the endless conveyor comprisesan endless grid screen supported on endless drive transmission means atopposite sides of said endless grid screen, characterised in that thereare provided at opposite sides of the endless grid screen pathway,endless drive transmission guide means formed and arranged so as todefine at least one cascade or step in the endless grid screen pathwayfor tumbling, in use of the grader, tubers passing over said cascade orstep thereby to provide the required movement of tubers on said gridscreen to facilitate the grading process.

Various suitable guide means are known in the art but conveniently thereare used guide means in the form of guide rollers or sprockets. Thesemay simply be used as pairs of more or less closely spaced guide rollersor sprockets defining a generally `S`-shaped pathway for the drivetransmission means. The latter may be in the form of a belt, chain,cable or other like flexible endless connector.

Thus by means of the present invention, movement of tubers on the newscreen and thereby improved grading efficiency, especially for elongatepotatoes, may readily be provided in an economic and effective mannerwith a significantly gentler action on the tubers.

A particular suitable form of endless grid screen for use in the graderof the present invention comprises a multiplicity of substantiallyparallel support bars bridging across spaced apart endless drivetransmission means with a multiplicity of generally `I`-shaped linkmembers with hollow cross-members bridging across pairs of successivesupport bars so as to define an endless grid screen with said barsextending through said hollow cross members, said hollow cross membershaving closely fitting male and female end portions for positivecoupling of adjacent link members so as to allow relative rotation atthe coupling whilst substantially maintaining dimensional stability ofthe grid screen openings in use of the endless grid screen, said hollowcoupled cross-members having a minimum internal diameter slightly largerthan the external diameter of said bars so as to allow relative movementbetween the grid screen link members and said support bars transverselyof the support bars at non-rectilinear portions of the grid screenpathway, thereby facilitating traversal of changes of direction in theendless grid screen pathway whilst maintaining dimensional stability ofthe grid screen openings.

It will nevertheless be understood that the abovedescribed endless gridscreen may also be used in other forms of graders, harvesters orseparators, apart from the grader of the present invention. Moreover theendless grid screen is not limited for use with tubers and may be usedwith a wide variety of other vegetables and fruits.

In order to provide an accurate grid screen opening size, and henceaccurate grading, it is important that that the link members should bemore or less accurately dimensioned. This can readily be achieved bymeans of suitable mass production techniques such as precision castingor moulding. Desirably the link members should be produced to within aprincipal dimensional tolerance of 0.25 mm, preferably 0.1 mm or less.Preferably the link members are formed of plastics materials e.g.polypropylene, polyamide, or polyvinylchloride, which are relativelylight, durable and gentle to tubers. Conveniently such plastics linkmembers are manufactured by injection moulding. The link members defineopenings which may have various shapes and/or configurations dependingupon the particular vegetable or fruit product to be graded. Thus forexample the openings may be square, rectangular, oval, round orpolygonal.

One problem that can arise, especially with elongate tubers, is thatthey can become jammed within the grid screen openings, projectingpartly therethrough. This can result in severe damage to these trappedtubers wherever the grid screen changes direction and/or when ittraverses a full width drive or return roller.

Thus in a further aspect, the present invention provides an endlessconveyor grader suitable for use in grading and separating tubers or thelike and having an endless grid screen with a predetermined openingdiameter, characterised in that there is provided, substantiallydirectly upsteam of a change of direction in the endless conveyorpathway, extending substantially across the width of the conveyor web ator in close proximity to the underside of the conveyor web, an ejectorroller having a large diameter of at least 2, preferably at least 3,times said predetermined opening diameter, for ejecting, in use of theseparator, tubers or the like which may have become jammed in the gridscreen openings.

Conveniently the ejector roller has a relatively smooth e.g. polished,substantially cylindrical surface, to allow sliding engagement withtrapped tubers in order to minimize damage thereto. Advantageously thereis used a driven ejector roller, said ejector roller preferably beingdriven in the same direction as the grid screen but at a slightly fasterspeed e.g. from 2 to 10% faster, desirably from 3 to 7% faster.

Advantageously an ejector roller is provided at each cascade or step ina grader of the present invention. Preferably the grader of the presentinvention is provided with at least 2 preferably from 3 to 6 cascades orsteps.

Preferably there is provided an overhead conveyor to assist passage oftubers or the like downwardly through the grid screen. The overheadconveyor engages the tubers helping to retain them on the grid screenand to spread them across the width of grid screen, as well as helpingto turn them on the grid screen, thereby assisting passage of the tubersthrough the grid screen. Moreover by varying the speed of the overheadconveyor relative to the grid screen, even to the extent of giving it areverse direction of movement, turning of the tubers can be increasedfurther. Futhermore by providing a non-planar surface topography e.g.ridges in the surface presented by fingers, pintles, bristles etc. ofthe overhead conveyor, spreading of the tubers can be further improved.

Most preferably said overhead conveyor is provided at least partlyupstream of said cascade or step. Such an overhead conveyor isparticularly advantageous where said tubers or the like are long andcurled or of an unusual irregular shape which do not readily passthrough said grid screen. Said overhead conveyor may be of any suitableform which can more or less positively engage and impart drive to tubersdisposed on said grid screen. Preferably said overhead conveyorcomprises an endless conveyor mounted on at least two return guides, andprovided with suitable drive means. Conveniently the guides are in theform of guide rollers, at least one of which is provided with a drivemeans formed and arranged for driving said endless conveyor. Thus theconveyor may be in the form of an endless belt having a surface ofresiliently deformable material, such as an open or closed cell foampolymeric material, e.g. a rubber sponge-like material. The use of sucha resiliently deformable material helps reduce damage to said tubersduring separation/grading.

In another form of overhead conveyor an endless belt or chain hasmounted thereon a plurality of spaced apart paddles or flights, or amultipicity of fingers or bristles, projecting downwardly into closeproximity with said grid screen so as to generally define compartmentsin which tubers on said grid screen may be captively retained on saidgrid screen.

It will be appreciated that whilst the overhead conveyor mayconveniently be in the form of a single flexible endless conveyorextending along and over said grid screen, it could alternatively be inthe form of a series of elements extending therealong e.g. a series ofgenerally cylindrical brushes all rotating in the same direction forsuccessively guiding and driving the tubers along said grid screen.

It will also be appreciated that the rate of flow of tubers over saidgrid screen may be controlled by adjusting the speed of the drive meansto said endless overhead conveyor.

Preferably the overhead conveyor is mounted above the grid screen insuch a way that its height above the grid screen can be varied with theaid of suitable height adjustment means thereby to accommodate differentsizes of tuber and to some extent control the variable transit time oftuber flow and the degree of separation/grading.

Preferably the conveyor is provided with resilient biasing means formedand arranged for holding the conveyor run of the conveyor down at adesired pre-determined height above the grid screen whilst allowingtransitory upward displacement thereof to pass over particularly largetubers or the like.

Conveniently there may be provided a plurality, desirably from two tofour, nested endless conveyor graders according to the invention,mounted with their grading reaches one above the other, the uppermostgrader having a larger grid screen opening then the grid therebelow andso on, so as to provide the ability to separate and grade a plurality ofdifferently sized tubers in a single grader/harvester/separator.

It will of course be appreciated that whilst the graders of the presentinvention are particularly suitable for use with tubers like potatoesthey may also be used with other materials in the form of discretebodies of randomly mixed size which it is desired to grade more or lessaccurately, such as other vegetables or fruits or minerals such as coal.

In a further aspect the present invention provides a method of gradingtubers or the like characterised in that said method comprises the stepsof: providing an endless conveyor grader of the invention, and conveyingsaid tubers or the like on said endless conveyor over said cascades orsteps.

Further preferred features and advantages of the present invention willappear from the following detailed description given by way of exampleof some preferred embodiments illustrated with reference to theaccompanying drawings in which:

FIG. 1 is a perspective view of a potato grader and separator in useseparating seed and ware potatoes;

FIG. 2 is a cutaway side elevation of the potato grader and separator inFIG. 1;

FIG. 3 shows a perspective partial view of a second embodiment of potatograder and separator, generally similar to that in FIG. 1;

FIG. 4 is a side view similar to that of FIG. 2 of the embodiment shownin FIG. 3;

FIG. 5 is a detailed side view of the potato grader in FIG. 3;

FIG. 6 is a partial detail plan view of the grid screen of the grader ofFIG. 1 on an enlarged scale; and

FIG. 7 is a detail transverse sectional view along a drive belt of agrid screen with a modified cross-bar mounting.

FIG. 1 shows a potato grader generally indicated by reference number 1in use for separating seed and ware potatoes 4. The grader and separator1 comprises a bulk hopper 2 into which are loaded harvested potatoes 4.The hopper 2 is provided with soil extraction rollers 6 which removeexcess soil 8 collected with the potatoes 4 and conveys the potatoes 4to a manual precleaning conveyor 10 where damaged or rotten potatoes aswell as large stones and other debris 12 which has been collected alongwith the potatoes 4 may be manually removed. The potatoes 4 then passonto the grader of the invention, indicated generally by referencenumber 20, where the potatoes 4 are agitated and small seed potatoes 4afall through an endless screen grid conveyor 21 of the grader 20 forremoval on a transversely mounted cross conveyor 22 which fills a box 24via a fall breaker 26 at the distal end 28 of the cross conveyor 22.Larger ware potatoes 4b do not fall through the grader 20 and arecarried thereon into a padded collection hopper 30 for separatecollection. As will be seen from FIG. 1 the potato grader and separator1 is provided with wheels 32 so that it may be moved from field to fieldor farm as required.

In more detail and with reference to FIG. 2 the grader 20 comprises aninclined framework 34 having a series of guide rollers 36 on which issupported the endless screen grid conveyor 21 which is supported ateither side by resiliently deformable endless drive transmission belts37. The belts 37 are driven by an electric motor 38 powered drive roller39.

To enable the screen to move easily and evenly round the drive rollerand especially the guide rollers 36, 39 with reverse flexing of thetraction or transmission belts 37 as they are bent first in onedirection and then in the opposite direction, it is an advantage to fixthe rods 47 (see also FIG. 6) of the screen grid conveyor 21 to thetraction belts 37 in the centre of the belt as opposed to riveted to thetop in conventional manner. This is done by moulding the traction beltaround the rod at the time of construction of the screem as shown inFIG. 7 and further described in our co-pending application No.PCT/GB94/00520.

The guide rollers 36 are arranged in pairs at opposite sides 23, 25 ofthe screen grid conveyor 21 for guiding engagement with the respectivebelt 37 at each side, with one roller 38 in each pair 36 at each sideabove, and one 39 below the belt 37 so as to define a generally `S` or`Z`-shaped path (depending on which side it is viewed from) for the belt37 and the screen grid conveyor 21. In this way a plurality of cascadesor steps 40 is formed in the screen grid conveyor 21 so that tuberspassing over the lip 42 of each cascade 40 tumble over onto the sectionof the screen grid conveyor 21 thereby being more or less gently tumbledto improve passage of smaller seed potatoes through the screen gridconveyor 21 directly onto the cross conveyor 22 or onto a secondaryconveyor 43 which carries them along onto the cross conveyor 22.

In order to prevent damage to any tubers which become jammed or trappedin the openings 44 in the screen grid conveyor 21, a large diameterpolished steel ejector roller 45 is mounted at the underside of theendless screen grid conveyor 21 immediately upstream of each cascade 40and extending across the full width of the screen grid conveyor 21--incontrast to the guide rollers 38, 39 which are disposed below and abovethe drive belts 37, only. The ejector rollers 45 are conveniently drivenby chain so that the outer cylindrical surface thereof travels at aslightly faster speed, ca. 5% faster, than the screen grid conveyor 21thereby to assist in the ejection of tubers projecting through thescreen grid openings 44 below the underside of the screen grid conveyor21.

FIGS. 3 to 5 show a second embodiment of potato grader generallyindicated by like reference numbers to those in FIGS. 1 and 2 with aprime added, for separating seed and ware potatoes 4¹. The grader andseparator 1¹ comprises a bulk hopper 2¹ (only partially shown) intowhich are loaded harvested potatoes 4¹. The hopper 2¹ is provided withsoil extraction rollers which remove excess soil 8¹ collected with thepotatoes 4¹ and conveys the potatoes 4¹ to a manual precleaning conveyor10¹ where damaged or rotten potatoes as well as large stones and otherdebris 12¹ which has been collected along with the potatoes 4¹ may bemanually removed. The potatoes 4¹ then pass onto the grader of theinvention, indicated generally by reference number 20¹ where thepotatoes 4¹ are agitated and small 4a and medium 4c sized potatoes 4¹fall through a first upper endless screen grid conveyor 21d of thegrader 20¹ onto second lower endless screen grid conveyor 21b of thegrader 20¹. The second lower screen 21b allows the smallest potatoes 4a¹to pass through for collection on a lower collection plate 29. Mediumsized potatoes 4c do not pass through the second lower screen 21b andare collected for removal on a transversely mounted cross conveyor 22¹which fills a box 24¹ via a fall breaker 26¹ at the distal end 28¹ ofthe cross conveyor 22¹. The largest 4b of the potatoes do not fallthrough either of first or second grid conveyors 21a, b of the grader20¹ and are carried thereon into a padded collection hopper (not shown)for separate, collection. As with the embodiment in FIG. 1 the potatograder and separator is provided with wheels 32¹ so that it may be movedaround as required.

The embodiment of potato grader shown in FIGS. 3 and 4 and as furtherdescribed with reference to FIG. 5 also has an overhead conveyor 55comprising an endless pintle 56 belt 57 mounted on two return rollers58, 59 one of which is driven by a motor (not shown). The overheadconveyor pintle belt 56 positively engages potatoes 4 on the upper gridconveyor 21a so as to turn and spread them on the screen grid therebyassisting passage of them through the upper screen grid 21a.

As shown in FIG. 6, the screen grid conveyor 21 comprises a large numberof generally "I"-shaped link members 46 mounted on cross-bars 47 whoseends 48 are secured by rivets 49 to drive belts 37 or inside thetraction belt to enable the rod to travel on a centre line of the beltFIG. 7. In more detail each link member has hollow tubular cross-pieces50 which are a loose clearance fit around the respective cross-bars 47.Each cross piece 50 has moreover at opposite ends 51, 52 male and femaleportions 53, 54 which are a close fit with opposite gender portions ofadjacent link members 46 so as to permit relative pivoting of coupledcross-pieces 50 substantially only about a common central longitudinalaxis of said cross-pieces 50 thereby to maintain dimensional stabilityof the openings 44 defined by the link members 46. (It will of course beappreciated that instead of cross pieces with opposite gender endportions there could instead be used alternating cross-pieces each withone or other gender i.e. male-male, female-female etc.)

As noted above, the tubular cross-pieces 50 are a loose clearance fitaround the cross-bars 47 i.e. have a minimum internal diameter 1 or 2 mmlarger than the external diameter of the latter. This allows therecti-linear link members 46 to be offset slightly as the belts 37 andcross-bars 47 secured thereto negotiate the arcuate path portionsdefined by the guide and return rollers.

FIG. 7 shows a detail transverse sectional view along a drive belt 37 ofa grid screen with a modified cross-bar 47 mounting.

For the avoidance of doubt it should be understood that the "grader" ofthe present invention may be used in all types of grading and separatingincluding field grading, pre-grading, seed and/or ware size grading,supermarket and other commercial distribution grading, in dedicatedgrading machinery, in separators and in potato harvesters, static ormobile, whether for potatoes or other like goods or produce.

I claim:
 1. An endless conveyor grader (1) suitable for use in gradingand/or separating tubers (4) or the like wherein the endless conveyor(21) comprises an endless grid screen (21) supported on endless drivetransmission means (37) at opposite sides (23, 25) of said endless gridscreen (21) for transmitting drive to said endless grid screen (21), andthere are provided, at opposite sides (23, 25) of a pathway followed bythe endless grid screen (21), endless drive transmission guide means(36, 39) for guiding said endless drive transmission means (37) in sucha way as to define at least one step (40) in the endless grid screenpathway, characterized in that the downstream side of the or each stepis inclined forwardly in the direction of travel of the endless gridscreen, with the base of the or each said step being spaced sufficientlyforward from the lip of the or each said step in order, during use ofthe grader (1), to cause tubers (4) passing over said lip of the or eachstep (40) to tumble over the grid screen (21) without falling ordropping generally vertically onto the screen, thereby providing therequired movement of tubers (4) on said grid screen (21) forfacilitating the grading and/or separating process.
 2. An endlessconveyor grader (1) as claimed in claim 1 wherein said endless drivetransmission guide means are in the form of pairs of more or lessclosely spaced guide rollers (36, 39) or sprockets defining a generally`S`-shaped pathway for said endless drive transmission means (37).
 3. Anendless conveyor grader (1) as claimed in claim 2 wherein said endlessdrive transmission means (37) is selected from a belt, a chain and acable.
 4. A endless conveyor grader (1) as claimed in claim 1 where saidendless grid screen (21) comprises a multiplicity of substantiallyparallel support bars bridging across said endless drive transmissionmeans (37) with a multiplicity of generally `I`-shaped link members (46)with hollow cross-members (50) bridging across pairs of successivesupport bars (47) so as to define an endless grid sreen (21) with saidbars (47) extending through said hollow cross members (50), said hollowcross members having closely fitting male (53) and female (54) endportions for positive coupling of adjacent link members so as to allowrelative rotation at the coupling whilst substantially maintainingdimensional stability of openings (44) provided in said grid screen (21)in use of the endless grid screen (21), said hollow coupledcross-members (50) having a minimum internal diameter slightly largerthan the external diameter of said bars so as to allow relative movementbetween the grid screen link members (46) and said support bars (47)transversely of the support bars at non-rectilinear portions of the gridscreen (21) pathway, thereby facilitating traversal of changes ofdirection on the endless grid screen (21) pathway whilst maintainingdimensional stability of the grid screen openings (44).
 5. An endlessconveyor grader (1) as claimed in claim 4 wherein said link members (46)of said endless grid screen have a principal dimensional tolerance of0.1 mm or less.
 6. An endless conveyor grader (1) as claimed in claim 5wherein said lint members (46) of said endless grid screen are made froma plastics material selected from polypropylene, polyamide orpolyvinylchloride.
 7. An endless conveyor grader as claimed in claim 6wherein said link members (46) of said endless grid screen defineopenings (44) having rectangular, oval, round or polygonalconfiguration.
 8. An endless conveyor grader as claimed in claim 7wherein said link members (46) of said endless grid screen are precisioncast or injection moulded.
 9. An endless conveyor grader (1) accordingto claim 4 wherein at least a portion of said endless grid screenpathway has a generally saw-toothed profile.
 10. An endless conveyorgrader (1) according to claim 9 wherein said generally saw-toothedprofile extends substantially horizontally.
 11. An endless conveyorgrader (1) according to claim 10, wherein the teeth of said saw-toothedprofile include obtuse angles.
 12. An endless conveyor grader (1)according to claim 9 wherein said openings (44) in said grid screen havea common predetermined opening diameter and the pitch of saidsaw-toothed profile is substantially greater than the predeterminedopening diameter of said grid screen openings.
 13. An endless conveyorgrader (1) according to claim 4, wherein the or each step comprises anupward slope at an effective tuber elevating angle and a downward slopeat an effective downward tuber conveying angle.
 14. An endless conveyorgrader (1) as claimed in claim 1 wherein said endless grid screen (21)is provided with a plurality of openings (44) having a commonpredetermined opening diameter and there is provided at a said step (40)an ejector roller (45) extending substantially across the width of theendless grid screen at or in close proximity to the underside of theendless grid screen, said ejector roller having a large diameter of atleast two times said predetermined opening diameter, for ejecting, inuse of the separator, tubers or the like which may become jammed in thegrid screen openings.
 15. An endless conveyor grader (1) as claimed inclaim 14 having from three to six said steps (40) defined in saidendless grid screen pathway.
 16. An endless conveyor grader (1) asclaimed in claim 15 provided with an overhead conveyor (55) having asurface configured so as to positively engage tubers (4) or the like onsaid endless grid screen (21) so as to turn and spread them on theendless grid screen thereby assisting tubers (4) or the like downwardlythrough said endless grid screen (21).
 17. An endless conveyor grader(1) as claimed in claim 16 wherein said overhead conveyor (55) is in theform of an endless belt (57) having a surface of resiliently deformablematerial.
 18. An endless conveyor grader (1) as claimed in claim 16wherein said overhead conveyor (55) is in the form of an endless belt(57) or chain having mounted thereon a plurality of spaced apart flightsprojecting downwardly into close proximity with said grid screen (21).19. An endless conveyor grader (1) as claimed in claim 16 wherein saidoverhead conveyor (55) is in the form of an endless belt (57) or chainhaving a multiplicity of finger (56) or bristle elements projectingdownwardly into close proximity with said grid screen (21).
 20. Anendless conveyor grader (1) as claimed in claim 16 wherein said overheadconveyor (55) comprises a plurality of generally cylindrical brushes forrotating in the same direction for guiding and driving tubers (4) or thelike along said grid screen (21).
 21. An endless conveyor grader (1) asclaimed in claim 20 provided with at least two nested endless conveyorgraders (21) according to claim 1 mounted with their grading reaches oneabove the other, the uppermost grader (21a) having a larger grid screen(21) opening (44) than the grader (21b) therebelow whereby a pluralityof differently sized tubers (4a, b, c) or the like may be separated andgraded in a single grader/harvester/separator.
 22. A harvesterincorporating an endless conveyor grader according to claim
 1. 23. Anendless conveyor grader (1) suitable for use in grading and separatingtubers (4) or the like and having an endless grid screen (21) which isprovided with a plurality of openings having a common predeterminedopening diameter,characterised in that there is provided, substantiallydirectly upstream of a change of direction in a pathway followed by theendless grid screen (21), extending substantially across the width ofthe endless grid screen at or in close proximity to the underside ofendless grid screen, an ejector roller (45) having a large diameter ofat least two times said predetermined opening diameter, for ejecting, inuse of the separator, tubers (4) or the like which may become jammed inthe grid screen (21) openings (44).
 24. An endless conveyor grader (1)as claimed in claim 23 wherein said ejector roller (45) has a largediameter three times said predetermined opening diameter.
 25. An endlessconveyor grader (1) as claimed in claim 23 wherein said ejector roller(45) has a smooth substantially cylindrical surface.
 26. An endlessconveyor grader (1) as claimed in claim 23, wherein said ejector roller(45) is driven at a speed of from three to seven per cent faster thanthat of said grid screen (21).
 27. A method of grading and/or separatingtubers or the like, characterized in that said method comprises thesteps of: providing an endless conveyor grader (1) according to claim 1,and conveying said tuners (4) or the like on said endless conveyor overthe or each said step (40) thereby tumbling the tubers (4) over on thegrid screen (21), without falling or dropping generally vertically ontothe grid screen (21) to provide the required movement of the tubers onsaid grid screen (21) for facilitating the grading and/or separatingprocess.